Engines operating on gaseous fuels, such as natural gas, are commonly operated on a lean air/fuel mixture to reduce generation of pollutants such as nitrous oxides (NOx). A lean air/fuel mixture is a mixture of air and fuel containing excess air beyond that which is stoichiometric for combustion. Often, industrial gas engines are operated at an air-fuel equivalence ratio, λ (lambda), of 1.85 or higher, where 1.0 is equal to stoichiometric. However, as the air/fuel mixture gets leaner, the speed at which the flame propagates through the mixture is slowed and the viability of the flame kernel is challenged. This can lead to lean misfire when the flame kernel is not robust enough to advance the flame front quickly, which can lead to very slow onset of combustion or complete misfire.
Passive prechamber igniters are often used to improve ignition. A prechamber igniter has an enclosure defining a prechamber over a spark plug, with no feed of fuel into the prechamber. However, often the air/fuel ratio in the prechamber becomes so lean that the adiabatic flame temperature cannot support the flame kernel, resulting in misfire in the prechamber or quenching of flame exiting the prechamber. The quenching phenomena, called sonic quenching, results when the prechamber pressure is high enough to cause sonic or near sonic flow of the flame out through the nozzles of the prechamber. The prechamber geometry can further exacerbate the problem by bulk quenching the flame temperature in the nozzles. The end result of the quenching is a potential misfire in the main combustion chamber.
Like reference symbols in the various drawings indicate like elements.